1. Technical Field
The present invention relates to protection circuitry and, more particularly, to a circuit for removing a peak reverse voltage generated from a power supply source.
2. Related Art
Generally, almost all electronic circuits are stressed by a surge of overvoltages of an impulse type or a transient of ringing voltages of a vibrating type which results from variations of output voltages from preceding circuits such as voltage generators. Such electronic circuits may be rectification circuits, inductance circuits including coils which generate a counter electromotive force according to current variations, and other auxiliary circuits which are connected to power supply sources for generating voltages varied in the form of pulses. The surge of overvoltages and the input of transient voltages may alter operation of the electronic circuits and shorten the life span of individual components of the electronic circuits. In some situations, the electronic circuits may be damaged extensively if the supply voltages are reversed.
Contemporary protection circuits against high transient overvoltages or forward and reverse surges of voltages are disclosed, for example, in U.S. Pat. No. 3,678,368 for Overvoltage Protection Arrangement For Power Converters issued to Popp, U.S. Pat. No. 3,733,519 for Protection Circuit For Regulated Power Supplies issued to Griffey, U.S. Pat. No. 4,271,445 for Solid-State Protector Circuitry Using Gated Diode Switch issued to Hartman et al., U.S. Pat. No. 4,462,069 for DC--DC Voltage Regulator Having An Input Protection Circuit, A DC--DC Inverter, A Saturable Reactor Regulator, And Main And Auxiliary Rectifying And Filtering Circuits issued to Becky, U.S. Pat. No. 4,689,713 for High Voltage Surge Protection For Electrical Power Line issued to Hourtane et al., and U.S. Pat. No. 4,910,654 for Current Limiting Scheme For The AC Input Circuit To A Switch Mode Power Supply issued to Forge. For DC--DC converters which include pulse voltage generators and rectification circuits, snubber circuits are generally used to provide protection against high transient overvoltages or forward and reverse surge of voltages across the rectification circuits. A typical snubber circuit is composed of either a charging capacitor connected in parallel across the rectification circuit, or a series of charging capacitor and resistor connected in parallel across the rectification circuit. However, the charging capacitor in both configurations is limited in capacitance and becomes instable due to heat. In addition, if the reverse surge of voltages exhibits a frequency higher than a specified frequency, the snubber circuit cannot effectively protect the rectification circuit from the reverse surge of voltages because the discharging time of the charging capacitor is limited.